MK Narayanan did not suffer any injuries and laughed off the incident.
A suspected member of pro-Tamil group, May 17, today threw a slipper at former National Security Adviser MK Narayanan during a programme in Chennai.
Mr Narayanan was attacked when he was leaving after his speech at an event organised by The Hindu Centre for Politics and Public Policy.
The former bureaucrat and ex-governor of West Bengal was attacked after he spoke on "The Future of Sri Lankan Tamil Refugees in India".
May 17, a pro-Tamil group, had already planned to protest near the venue.
Police have detained the attacker, Prabhakaran, believed to be from Tamil Nadu's Pudukottai district.
Meanwhile, Mr Narayanan did not suffer any injuries and laughed off the incident, sources said.